This invention relates to short-circuit protected switched output circuits. Such arrangements are used in automotive applications, for example to switch driving currents to inductive loads such as relays.
In a typical such short-circuit protected switched output circuit it is known to use a comparator coupled to the circuit's output node and to a reference voltage. The comparator is arranged to function as an oscillator producing an output signal having a low frequency, low duty-cycle signal at the output node in the event of the output node being short-circuited. Such a known short-circuit protected switched output circuit is shown in FIG. 1 of the accompanying drawings.
As will be seen in FIG. 1, an output switching transistor Q1 has its current electrodes coupled respectively to a load and to a ground connected resistor R9, and has its control electrode connected to the output of a differential voltage comparator U1A. The negative input (-) of the comparator is coupled to the ground-coupled electrode of transistor Q1 via a diode D1 and to a reference voltage node via a potential divider network. The positive input (+) of the comparator is coupled to a command signal node and to a supply voltage (VCC) node via a feedback path from the comparator output.
Such a known short-circuit protected switched output circuit is subject to a number of disadvantages: the circuit is subject to power dissipation in the resistor R9 coupling the switching transistor Q1 to ground and in the protection circuitry through which the switch is driven.